In recent years, LEDs are used as light sources for lighting instead of fluorescent lamps. For example, a document 1 (Japanese Patent Publication Laid-Open No. 2009-43447) discloses an LED lamp which has a similar shape as a prior straight tube fluorescent lamp. This LED lamp includes a light source block including a mounted substrate formed into a strip shape and multiple LEDs mounted on the mounted substrate, a glass tube in the form of a straight tube configured to accommodate the light source block, caps fastening opposite open ends of the glass tube, and terminal pins projecting from aspects of the caps and used for supplying electrical power to the light source block. Such an LED lamp is detachably coupled to lamp sockets provided on a dedicated lighting fixture, and lights in response to power (DC power) supply from an LED lighting device provided on the lighting fixture through the lamp sockets.
Further, a document 2 (Japanese Patent Publication Laid-Open No. 2006-10271) discloses a prior instance regarding LED lighting devices. The prior instance disclosed in the document 2 detects a voltage (output voltage) provided to an LED lamp (a lamp socket) and a current (output current) flowing through an LED lamp, and performs control (constant-current control) of regulating the output voltage such that the output current becomes identical to a target value (e.g., a rated current of the LED lamp). When the LED lamp is detached from the lamp socket while the LED lighting device is in operation, the LED lighting device limits its output voltage not greater than a predetermined upper limit (referred to as a no-load voltage) in order to prevent an abnormal increase in the output voltage.
Between an electrode of the lamp socket and the terminal pin of the LED lamp is applied a DC voltage which exceeds tens of volts. Therefore, an arc discharge is likely to be developed between the electrode of the lamp socket and the terminal pin when the LED lamp is detached from the lamp socket. When the constant-current control is performed under the occurrence of the arc discharge, the output voltage is increased up to the no-load voltage. In this situation, the arc discharge may be difficult to extinguish.
When the LED lamp is coupled to the lamp socket while the LED lighting device is in operation, the constant-current control may cause an increase of the output voltage until the current flowing through the LED lamp becomes equivalent to the target value, and the output voltage may be equivalent to the no-load voltage. Consequently, in order to shorten a time of a continued arc discharge, the output voltage may be lowered when the output voltage reaches the no-load voltage. With this instance, the LED lamp may not be turned on successfully in response to attachment of the LED lamp to the lamp socket.